ESO-VLT/FLAMES: control software for a multi-object observing facility

FLAMES is a complex observational facility for multi-object spectrography installed at ESO VLT UT2 telescope at Paranal. It consists of a Fibre Positioner that feeds GIRAFFE, a medium-high resolution spectrograph, and UVES, a high resolution stand-alone spectrograph operational in slit mode since 1999. The Positioner is the core component of FLAMES. It is a rather large and complex system comprising two spherical focal plates of approx. 90 cm in diameter, an exchanger mechanism, R-θ robot motions and a pneumatic gripper mechanism with a built in miniature CCD camera. The main task of the Positioner is to place a fibre (button) at a given focal plate position with accuracy better than 40 microns. The fibre positioning process is performed on the plate attached to the robot while an observation is being performed on the plate attached to the telescope rotator. The whole instrument is driven by software designed in accordance with the VLT Common Software standards, allowing the complete integration of the instrument in the VLT environment. The paper mainly focuses on two areas: the low level control and the performance of the Fibre Positioner; and the high level coordinating software architecture that provides facility for parallel operations of multiple instruments.